1. Field of the Invention
The present invention relates to a joint for connecting and coupling a double pipe which consists of an inner pipe for transporting a fluid, and an outer pipe that covers the inner pipe for the purpose of prevention of leakage or the like, i.e., a double-pipe joint.
2. Explanation of Related Art
As means for connecting a pipe for transporting a fluid to a fluid apparatus such as a valve or a pump, or to a similar pipe, usually, a pipe joint is used as disclosed in Japanese Patent Application Laying-Open No. 6-129575. Such a pipe joint is requested to have a function of connecting a pipe to a joint body so as not to cause leakage of a fluid flowing through the pipe. The pipe joint disclosed in Japanese Patent Application Laying-Open No. 6-129575 is configured so that a union nut is screwed with a joint body into which a pipe made of a synthetic resin is fitted, whereby a diameter-increased pipe end portion can be connected in a locked state.
For example, as means for protecting a pipe or a pipe joint to which the pipe is connected from a damage due to a collision against another article, or means for preventing a fluid from leaking in the case where a crack or a damage is produced by any cause, it is contemplated to dispose an outer pipe which surrounds the pipe or the pipe joint, and an outer-pipe joint for connecting and coupling the outer pipe. In this contemplation, it is required that the pipe is formed by a double pipe consisting of an inner pipe for transporting a fluid, and an outer pipe for protecting the inner pipe, and the pipe joint is formed by a joint for a double pipe, i.e., a double pipe joint which comprises a joint for the inner pipe and that for the outer pipe.
With respect to such a double pipe joint, for example, a joint disclosed in Japanese Patent Application Laying-Open No. 2001-235080 serves as a reference. The publication discloses a structure in which an inner pipe and an inner-pipe joint are covered by an outer pipe and an outer-pipe joint, thereby protecting the inner pipe and the inner-pipe joint. The inner-pipe joint and the outer-pipe joint are separately configured, and formed as structure members which are independent from each other. However, the means disclosed in Japanese Patent Application Laying-Open No. 2001-235080 has a structure in which the inner-pipe joint and the outer-pipe joint do not interfere with each other. In order to hold the inner-pipe joint to a predetermined position or posture, therefore, it is necessary to use a double pipe having a special structure in which the inner pipe is supported by the outer pipe as disclosed in FIG. 5 of Japanese Patent Application Laying-Open No. 2001-235080. This is disadvantageous in cost, and also in that the diameter of the doubled pipe joint portion is significantly large (the size is increased).
In the case where a double pipe consisting of two or inner and outer pipes is used in piping for the purpose of concurrently flowing two different kinds of fluids or protecting a pipe for transporting a fluid, it is preferably to employ a useful double-pipe joint having an advantage that it has a function of supporting the inner and outer pipes in a predetermined relative positional relationship, or that the whole pipe joint is compactified. Therefore, a double-pipe joint having such an advantage is desired.